import java.util.LinkedList;
import java.util.Queue;
//两个队列实现栈
public class MyStack {
    private Queue<Integer> queue1 ;
    private Queue<Integer> queue2 ;

    public MyStack() {
        queue1 = new LinkedList<>();
        queue2 = new LinkedList<>();
    }

    public void push(int x) {
        if(!queue1.isEmpty()){
            queue1.offer(x);
        }else if(!queue2.isEmpty()){
            queue2.offer(x);
        }else{
            queue1.offer(x);
        }
    }

    public int pop() {
        if(empty()){
            return -1;
        }
        if(!queue1.isEmpty()){
            int size = queue1.size();
            for (int i = 0; i < size - 1 ; i++) {
                queue2.offer(queue1.poll());
            }
            return queue1.poll();
        }else{
            int size = queue2.size();
            for (int i = 0; i < size - 1 ; i++) {
                queue1.offer(queue2.poll());
            }
            return queue2.poll();
        }
    }

    public int top() {
        if(empty()){
            return -1;
        }
        int val = -1;
        if(!queue1.isEmpty()){
            int size = queue1.size();

            for (int i = 0; i < size  ; i++) {
                val = queue1.poll();
                queue2.offer( val);
            }
            return val;
        }else{
            int size = queue2.size();
            for (int i = 0; i < size  ; i++) {
                val = queue2.poll();
                queue1.offer( val);
            }
            return val;
        }
    }

    public boolean empty() {
        return queue1.isEmpty() && queue2.isEmpty();
    }
}
